In 1981, Philips and Sony proposed physical standards and format standards for digital audio compact disks (CD-DA). Since then, disks complying with the same general physical specifications for audio compact disks have been introduced for general digital data storage and distribution. Data on the disks may be formatted in a variety of ways, including the original format for digital audio, a format for computer read-only-memory (CD-ROM) and special formats for interactive multimedia, video, and digitized photographs.
There is a general need for interchange compatibility among media and drives so that drives can read or write (if appropriate) any type of compact disk and any particular compact disk can be read or written (if appropriate) in any drive. However, general interchange compatibility is impeded by both physical obstacles and logical format obstacles. For an example of a physical obstacle, the maximum reflectance for rewritable media is about one-third the maximum reflectance for read-only and write-once media. As a result, drives capable of reading rewritable media must have a gain switch or automatic gain control in order to read all types of disks. CD-ROM drives are presently being designed (but not yet widely available) for reading rewritable media when it becomes widely available. Logical format obstacles result from a need to adapt to the needs and advantages of previously unforseen or unplanned applications (for example, rewritable media) while maintaining backward compatibility with previous formats.
Typically, a data mass memory medium is logically formatted into addressable units. For example, computer disks and data tapes typically have numbered sectors and numbered tracks. In addition, data mass memory typically includes overhead information including additional bits for error detection and correction, bits for synchronization of a clock before reading or writing, and unused space for accommodating variable speeds among drives. Typically, overhead information (including sector addresses, synchronization patterns and gaps) is written separately in a process called formatting. Typically, formatting must be completed before any variable data are written. Formatting often takes a substantial amount of time. Therefore, media such as flexible disks and tapes are often formatted by the manufacturer. This increases the cost of the media but is a great convenience to the customer. Sometimes, flexible disks and tapes may also be formatted or re-formatted in a drive. As will be explained in more detail below, formatting rewritable compact disks requires a significant amount of time and presents some unique challenges.
Before discussing compact disk formatting, some terminology definitions are required. All compact disks have a single spiral data track, starting near the center of the disk and ending near the edge of the disk. In the case of recordable and rewritable media, the spiral track is a physical groove. In the case of read-only media, the physical data track may be called a "groove" even though there is no physical groove. In addition to the physical track, data may be formatted into logical tracks. In this patent document, tracks will always be expressly identified as physical or logical. The physical track may be called a groove where appropriate.
In some compact disk formats, bytes are organized into frames and frames are organized into sectors, where a sector is the smallest addressable unit. In other formats, the terms sector, frame and block are somewhat interchangeable. In this patent document, a frame is the smallest addressable unit. A frame has 2,352 data bytes. Frame addresses are expressed in units of time and frame offset. A frame address is expressed as {M,S,F}, where M is minutes, S is seconds, and F is a frame offset within a second. There are 75 frames per second, 60 seconds per minute. An MSF address may be absolute (measured from the beginning of the physical track) or relative (measured from the beginning of the current logical track). Frames may be organized into packets. A packet has a link frame, four runin frames, actual data frames, and four run-out frames. Recordable media has variable length packets. For rewritable media, the current format standard requires packets that are fixed length with 39 total frames per packet (32 actual data frames and 7 overhead frames). The number 39 is an arbitrary specification, and in this patent document, the term "packet aligned" is intended to include any standard number of frames per packet.
The format for CD-DA and CD-ROM media requires an area near the beginning of the physical track called a lead-in, followed by a program area. The program area is formatted into logical tracks. Finally, the format requires an area at the end of the last logical track called a lead-out. CD-DA and CD-ROM drives can seek to a specific logical track number. The lead-in area includes a table of contents (TOC), which includes a table of absolute MSF starting addresses for the logical tracks. The lead-in area also contains a pointer to the lead-out area. Many drives cannot calibrate radial position, and therefore cannot read a medium, unless both the lead-in and lead-out are present.
Recordable and rewritable media have a physical groove in which data are recorded. Read-only (CD-DA and CD-ROM) media do not have physical grooves but the spiral path of data pits and lands does provide a path that can be optically detected. For radial movement, many drives count the number of times a read head crosses the spiral data track for read-only media or the physical groove for recordable or rewritable media. Drives for recordable and rewritable media can always detect a physical groove but CD-DA and CD-ROM drives may not be adapted to detect physical grooves. For some drives, radial movement across the spiral physical track may be open loop without counting physical track crossings. Drives having open loop radial movement typically seek from the lead-in area to the lead-out area to calibrate the radial servo system. Therefore, for some drives, all frames between lead-in and lead-out must be formatted.
After formats were developed for CD-DA and CD-ROM, recordable (also called write-once) media (CD-R) were introduced. Of particular importance to CD-R recording is an ability to partially record a disk, and then later append new data. A single lead-in is not sufficient, since for write-once media the original lead-in cannot be modified when new data are added. Therefore, the technique of "sessions" was introduced, in which the physical track is formatted in multiple sessions with each session having a lead-in and a lead-out. Each disk may have up to 99 logical tracks across all sessions. Each lead-in except the last contains a pointer to the frame address of the next (possible) session. CD-ROM media formats and other formats may now be multi-session.
Still later, rewritable (also called erasable) media (CD-RW) were developed. With CD-RW, as with magnetic disks and tapes, there is need for generalized random access recording. However, backward compatibility needs to be maintained with single-session (e.g., CD-DA) and multi-session disk formats.
For tapes and disks, special formatting magnetic heads can be manufactured for simultaneously formatting many tracks and for formatting at a faster than normal track speed. However, for CD-RW media, writing each bit requires heat and a fixed cooling rate, which is inherently slow. Rewritable media uses a phase change material having a transparency that can be reversibly changed by heating, and then cooling at a controlled rate. A laser is used to heat, and then cool small areas at the required controlled rate. Formatting an entire CD-RW disk takes 40-80 minutes, whether done by the media manufacturer or in a drive. As a result, pre-formatted CD-RW media may be prohibitively expensive for the customer. However, keeping a customer's drive busy for 40-80 minutes to format a disk when the customer needs to immediately record data may also be commercially unacceptable. There is a general need for fast partial formatting of CD-RW media by a drive to accommodate quick initial useability and incremental recording.
There are many organizations involved with standards or defacto standards for CD media and formats, including ANSI, IEC, ISO, Philips and Sony. Of particular interest is Optical Storage Technology Association (OSTA), 311 East Carrillo Street, Santa Barbara, Calif. 93101. OSTA maintains an industry accepted file system standard called Universal Disk Format (UDF). UDF specifications permit incremental writing on a partially formatted CD-RW disk. In addition, OSTA, Philips, and Hewlett-Packard Company are jointly developing specifications for logical devices and physical requirements for drive manufacturers, computer manufacturers, and operating system software developers so that any operating system or drive can read all the following types of media: CD-DA, CD-ROM, CD-R, and CD-RW. Among other things, these specifications, called MultiRead, specify drive requirements to accommodate the reflectivity of CD-RW media.
FIGS. 1A-1C and FIG. 2 illustrate the UDF specified process for incremental formatting and writing. FIGS. 1A-1C depict the formatted areas on the physical track of the disk. FIG. 2 is a flow chart of the method of incremental formatting depicted in FIGS. 1A-1C. In FIG. 1A, a physical track has been partially formatted, with a lead-in area 100, a program area 102 and a lead-out area 104. When the capacity of the program area 102 is exceeded, the host computer commands the drive to extend the formatted area as illustrated in FIG. 1B. Note, in general in this patent document, formatting can be accomplished by either an explicit format command or implied by a write command. New frames 108 are formatted with null data, where null data may be zeros or any other arbitrary value, starting at the location of the old lead-out area (104). The old lead-in area 100 is updated (overwritten or optionally erased and overwritten) to provide a new lead-in area 106 and a new lead-out area 110 is appended. After incremental formatting, in FIG. 1C, the new data 112 are written in the newly formatted frames.
In FIG. 2, a host computer first sends a command (200) to an idle drive (202) to partially format a blank disk. In step 204, the drive partially formats a disk with lead-in, program, and lead-out as depicted in FIG. 1A. Next, after detecting that the disk cannot hold new data that the host needs to write, the host computer (using UDF) sends a command (206) to incrementally format additional space. The additional space may optionally be greater than what is required to write the new data. The drive then formats new frames with null (arbitrary) data (208), writes new lead-in and lead-out areas (210). The host computer then sends the new data (212) and the drive writes new data in the newly formatted frames (214). As a result, each time the disk space needs to be expanded, in addition to simply writing the new data, a substantial amount of overhead time is required for formatting frames with null (arbitrary) data and rewriting the lead-in and lead-out areas.
There is a need for faster partial formatting, faster incremental recording, and improved customer convenience for CD-RW disks, preferably with minimal changes to drives, operating system software, and interchange standards.